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Retention Time of Lakes in the Larsemann Hills Oasis, East

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Retention Time of Lakes in the Larsemann Hills Oasis, East Retention time of lakes in the Larsemann Hills oasis, East Antarctica Elena Shevnina1, Ekaterina Kourzeneva1, Yury Dvornikov2, Irina Fedorova3 1Finnish Meteorological Institute, Helsinki, Finland. 2 Department of Landscape Design and Sustainable Ecosystems, Agrarian-Technological Institute, RUDN University, 5 Moscow, Russia 3Saint-Petersburg State University, St. Petersburg, Russia. Correspondence to: Elena Shevnina ([email protected]) Abstract. The study gives first estimates of water transport time scales for five lakes located in the Larsemann Hills oasis (69º23´S, 76º20´E) in East Antarctica. We estimated the lake retention time (LRT) as a ratio of the lake volume to the inflow 10 and outflow terms of a lake water balance equation. The LRT was evaluated for lakes of epiglacial and land-locked types, and it was assumed that these lakes are monomictic with water exchange existing during the warm season only. We used hydrological observations collected in 4 seasonal field campaigns to evaluate the LRT. For the epiglacial lakes Progress and Nella/Scandrett, the LRT was estimated at 12–13 and 4–5 years, respectively. For the land-locked lakes Stepped, Sarah Tarn and Reid, our results show a big difference in the LRT calculated from the outflow and inflow terms of the water balance 15 equation. The LRT for these lakes vary depending on the methods and errors inherent to them. We suggest to rely on the estimations from the outflow terms since they are based on the hydrological measurements with better quality. Lake Stepped exchange water within less then 1.5 years. Lake Sarah Tarn and Lake Reid are endorheic ponds with the water loss mainly through evaporation, their LRT was estimated as 21–22 years and 8–9 years, respectively. To improve the estimates of the LRT, the special hydrological observations are needed to monitor the lakes and streams during the warm season with the 20 uniform observational program. 1 Introduction Antarctica is the continent, where most of water is frozen and deposited in the ice sheets, glaciers and permafrost. It makes the continent sensitive to climate warming by enhancing a transition of water from solid to liquid phase (melting). Melted water accumulates in lakes and streams, which appear on the surface of the continental ice sheet, at its contact with rocks 25 and in local depressions in ice free areas (oases). Antarctic lakes exist under the ice sheet (subglacial type lakes) and on top of it (supraglacial type). Many lakes are located on the boundary between the rocks and continental/shelf ice sheets (epiglacial and epishelf types). In oases, lakes of the land-locked or closed basin type occupy local relief depressions (Govil et al., 2016; Hodgson, 2012). In warm seasons, numerous supraglacial lakes appear on the surface of the continental ice sheet over its edges, in “blue ice” 30 regions, and in the vicinity of rock islands or nunataks (Leppäranta et al., 2020; Bell et al., 2017). These lakes may be up to 1 80 km long, and accumulate large amounts of liquid water potentially affecting the ice discharge, ice calving and hydro- stability of the continental ice sheet (Stokes et al., 2019;). Lakes of the epiglacial type are situated at glacier edges, and melting of the glacier ice is the main source of water inflow to them. These lakes may be perennially frozen, or partially free of ice during the austral summer lasting from December to February. Land-locked lakes appear after retreat of the 35 continental ice sheet in local depressions. Precipitation and melting of seasonal snow cover are two main sources of water inflow for these lakes. Precipitation over the lake surface usually contributes insignificantly to the water inflow compared to the snow melting (Klokov, 1979). Land locked lakes are ice-free for a period of 2–3 months in summer, and they mostly lose water through the surface runoff in the outlet streams, and/or through evaporation over their surface. In our study, we focus on two types of lakes, namely epiglacial and land-locked, located in the ice free area of the Larsemann Hills oasis, 40 East Antarctic coast. Water chemical composition and presence of living forms in Antarctic lakes are strongly linked to their thermal regime and water balance (Castendyk et al., 2016; Bomblies et al., 2001). Among other parameters, water transport/exchange time scales are needed to study lake eutrophication, bio production and geochemical processes by numerical modelling (Nuruzzama et al., 2020; Geyer et al., 2000; Foy, 1992; Burton, 1981). The lake retention time (LRT), also called “the 45 flushing time” in Geyer et al. (2000) or “the coefficient of water external exchange” in Doganovsky and Myakisheva (2015), is among other transport scales to be taken into account while modeling the water exchange and mixing processes in lakes and estuaries (Monsen et. al., 2002; Lincoln et al., 1998). It indicates the time period of water renewing in the lake (Pilotti et al., 2014; Rueda et al., 2006) and is usually expressed in years. There are only few studies addressing estimates of water transport scales for the Antarctic lakes, mostly due to lack on the hydrological observations. For example, Foreman et 50 al. (2004) give the hydraulic residence time (which is the same as the LRT) for three lakes located in the Dry Valleys, West Antarctica; Loopman and Klokov (1988) suggest estimations of the coefficient of water external exchange (which is the inverse of the LRT) of six lakes located in the Schirmacher oasis, East Antarctica. This study contributes to estimations of the LRT of lakes located in the Larsemann Hills oasis, East Antarctica. Water temperature regime, chemical composition, and biota of the local lakes have been actively studied since 1990s (Hodgson et 55 al., 2006 and 2005; Verleyen et al., 2004 and 2003; Saabe et al., 2004 and 2003; Kaup and Burgess, 2002; Gasparon et al., 2002; Burgess and Kaup, 1997). However, understanding of the seasonal water cycle of these lakes is still weak due to serious gaps in the hydrological measurements on the lakes. It limits the applicability of mass/water balance and biogeochemical models (Nuruzamma et al., 2020; Kaup, 2005). This study focuses on the lakes Stepped, Nella/Scandrett, Progress, Sarah Tarn and Reid since their water resources and biogeochemistry are important for human activity (Sokratova, 60 2011; Burgess and Kaup, 1997; Burgess et al., 1992). Hydrological data collected during four summer seasons in years 2011–2017 were used to calculate the LRT. 2 1. Study area The Larsemann Hills occupy an area of approximately 50 square kilometres on the sea shore of the Princess Elizabeth Land, East Antarctica. The area consists of the Stornes, Broknes and Mirror peninsulas, together with a number of small islands in 65 Prydz Bay. The peninsulas are rocks exposed by glacial retreat since the Last Glacial Maximum (Hodgson et al., 2005). The basement geology consists of the composite of orthogneisses overlying various pegmatites and granites (Geological map, 2018; Carson et al., 1995). Climate of the Larsemann Hills is influanced by katabatic winds blowing from the north-east during most of austral summer. In this period, the daytime air temperatures frequently exceed 10 C,̊ with the mean monthly temperature of about 0 70 C.̊ Mean monthly winter temperatures range between –15 C̊ and –18 C.̊ The annual precipitation amount is 159 mm (statistics is taken from the Russian Arctic and Antarctic Research Institute, http://www.aari.aq). Rain is rarely observed over the ice free areas also known as oases. There are two meteorological stations in the Larsemann Hills. Zhongshan station (WMO index 89573) started operating in 1989, and Progress station (89574) operated intermittently from 1988– 1998, and since 1999 started to provide continuous observations (Turner and Pendlebury, 2004). Local climatology for the 75 period of 1988–2010 is reported by the Russian Arctic and Antarctic Research Institute from the Progress station, see Table 1 in Shevnina and Kourzeneva (2017). Yu et al. (2018) notice the increasing trends for the annual precipitation for the period of 2003–2016. There are more than 150 lakes in the Larsemann Hills oasis. Many of them occupy local depressions formed after melting of the continental ice sheet (Gillieson et al., 1990). The lake water chemical composition is affected by sea sprays, local 80 geology and periodic seawater surges caused by calving of the Dålk glacier situated next to the east corner of the oasis (Kaup and Burgess, 2002; Stüwe et al., 1989). The majority of lakes are monomictic, which means that they are thermally homogeneous during summer, also due to persistent katabatic winds (Bian et al., 1994). The land-locked and epiglacial lakes are typical for the coastal ice free areas such as the Larsemann Hills oasis. The land-locked lakes are usually small ponds (Lake Stepped, Lake Sarah Tarn and Lake Reid in the Fig. 1). 85 Figure 1: Lakes on the Mirror peninsula, the Larsemann Hills, East Antarctica: A: the red box indicates the location of the oasis; B: the red lines outline the catchment areas represent the lakes considered in this study according to the digital map scale of 1:25000, AAD, 2005;t he LIMA composite is on the background map(Bindschadler et al., 2008). 90 Land locked lakes are free of ice in December–February, and their water temperatures reach 10.0–11.0 °C in January (Boronina et al., 2019; Gillieson et al., 1990). Lake Stepped is located in the old coastal lagoon, and connected to the sea through the underground leakage of water. During the warm period, on outlet stream in the north-eastern corner of the lake releases water surplus. Water surplus occurs due to melting of the seasonal snow cover in the lake catchment.
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